Active noise control (ANC) technology of canceling noise by sound of an opposite phase is known (refer to NTL1). There are several control methods for ANC. For example, in a feedforward type, ANC control is performed using a reference microphone, an error microphone, and a secondary sound source speaker.
The reference microphone detects a reference signal (for example, audio as a noise source). The error microphone is a microphone for observing a noise reduction effect. The secondary sound source speaker outputs pseudo noise to cancel out the noise. The signal detected by the reference microphone is processed through a noise control filter, and becomes the pseudo noise output from the secondary sound source speaker. The coefficient of the noise control filter is adjusted by mutual cancellation of the noise and the pseudo noise so that the error signal detected by the error microphone is minimized.
In order to sufficiently reduce the noise using the ANC, it is necessary that a microphone (reference microphone or error microphone) and a speaker (secondary sound source speaker) are operating normally. As a technique for detecting abnormality in the microphone and the speaker, a disconnection detection circuit disclosed in PTL 1 is known. The disconnection detection circuit picks up sound output from a single speaker with a single microphone, and detects disconnection of the speaker and the microphone by comparing a speaker signal and a microphone signal.
However, in a case where there are a plurality of microphones and speakers in a vehicle, it is difficult to carry out an abnormality test of the microphone and the speaker in a short time.
An object of the present disclosure is to shorten time required for the abnormality test of a speaker and a microphone to determine presence or absence of abnormality even in a case where there are a plurality of microphones and speakers in a vehicle.